By default, mod_translation prefixes each URL (using
URL rewriting) in your website with the code of the
current language. The idea behind this is that each language version
of a resource gets its own URL, and is as such indexable for
Google.

This behaviour is enabled by default, but can be switched off in the
admin, by going to Structure, Translation. There is a checkbox at
the bottom of the page.

Alternatively you can set the config key
mod_translation.rewrite_url to false.